A new method for determination of self-cleaning activity of photocatalytic surfaces is proposed. It is based on the deposition of a transparent solid layer comprising terephthalic acid over the photocatalytic surface (three types of titania films on glass were used as test samples). When such a system was irradiated, among the other degradation products also a hydroxyterephthalic acid was formed due to a reaction between photoexcited TiO(2) and terephthalic acid. Hydroxyterephthalic acid is a highly fluorescent molecule and it was detected by HPLC-FLD or spectrofluorimeter. This direct method of following quantitatively the formation of an oxidation product was found to be accurate, highly sensitive and reproducible, therefore, it represents a promising option to be considered in standardization efforts in the field of photocatalysis. (C) 2010 Elsevier B.V. All rights reserved.